Self pressurizing bladder tooling

ABSTRACT

A method of fabricating a composite structure includes laying at least one composite ply about a bladder, the bladder comprising a phase change material in a first phase having a first volume, positioning an outer mold about the bladder and the at least one composite ply, and curing the at least one composite ply to form the composite structure. Curing causes the phase change material contained within the bladder to change to a second phase to expand from the first volume to a second volume and apply a pressure to an interior surface of the composite ply and press an outer surface of the composite ply against the outer mold to form an interior cavity. The bladder is not removable from the formed interior cavity.

BACKGROUND

Embodiments of the disclosure relate to the manufacture of highstrength, light weight parts made of composite materials, and moreparticularly, to a system and a method for fabricating complex hollowcomposite structures.

Composites have proven to be very useful materials, especially in thefield of aviation. Weight is a very important and sensitive subject andany method to limit or reduce it is valuable.

Complex composites structures often require specialized tooling to formtrapped geometries. In the past, multi-piece hard tools, bladders, andwashout mandrels have been used to provide internal support during thecure of the composite structure. With respect to multi-piece hard tools,provisions for removal of the tooling must be established, therebylimiting the types of parts that can be made. In addition, mandrels needaccess to wash out solid material after a curing process, and thereforecomplete removal can be an issue. Bladders typically require ports toprovide a means for pressurizing and depressurizing the bladder duringprocessing. Accordingly, none of the existing mechanisms provide a meansof establishing an internal support for a fully enclosed volume of acomposite structure.

BRIEF DESCRIPTION

According to an embodiment, a method of fabricating a compositestructure includes laying at least one composite ply about a bladder,the bladder comprising a phase change material in a first phase having afirst volume, positioning an outer mold about the bladder and the atleast one composite ply, and curing the at least one composite ply toform the composite structure. Curing causes the phase change materialcontained within the bladder to change to a second phase to expand fromthe first volume to a second volume and apply a pressure to an interiorsurface of the composite ply and press an outer surface of the compositeply against the outer mold to form an interior cavity. The bladder isnot removable from the formed interior cavity.

In addition to one or more of the features described above, or as analternative, in further embodiments curing the at least one compositeply further comprises changing a temperature adjacent the at least onecomposite ply.

In addition to one or more of the features described above, or as analternative, in further embodiments comprising at least partiallyfilling an interior chamber of the bladder with the phase changematerial in the first state prior to laying the at least composite plyabout the bladder.

In addition to one or more of the features described above, or as analternative, in further embodiments in the first phase, the material isa liquid and in the second phase the material is a gas.

In addition to one or more of the features described above, or as analternative, in further embodiments in the first phase, the material isa solid and in the second phase the material is a gas.

In addition to one or more of the features described above, or as analternative, in further embodiments an exterior surface of the bladderdefines a contour of an interior surface of the composite structure whenin the inflated configuration.

In addition to one or more of the features described above, or as analternative, in further embodiments an interior surface of the outermold defines a contour of an exterior surface of the compositestructure.

In addition to one or more of the features described above, or as analternative, in further embodiments after curing the at least onecomposite ply is completed, the bladder including the material remainssealed within the at least one composite ply.

In addition to one or more of the features described above, or as analternative, in further embodiments comprising removing the materialfrom the bladder while the bladder remains within the compositestructure.

In addition to one or more of the features described above, or as analternative, in further embodiments comprising: removing the pressureapplied by the material to the interior surface of the bladder aftercuring of the at least one composite ply is complete and removing thematerial from the composite structure.

According to yet another embodiment, a composite structure includes atleast one composite ply defining a cavity, and a bladder arranged withinthe cavity such that the at least one composite ply is wrapped about thebladder. The bladder includes a flexible body operable to define aninterior surface of the composite structure, the body having a hollowchamber and a phase change material arranged within the hollow chamber.The phase change material is in a first phase having a first volume whensupplied to the hollow chamber and the phase change material is in asecond phase having a second volume during a cure of the at least onecomposite ply wrapped about the bladder. The second volume is expandedrelative to the first volume, and wherein the bladder is not removablefrom the cavity.

In addition to one or more of the features described above, or as analternative, in further embodiments in the second phase, the phasechange material is configured to apply a pressure to an interior surfaceof the bladder.

In addition to one or more of the features described above, or as analternative, in further embodiments in the first phase the phase changematerial is a liquid and in the second phase the phase change materialis a gas.

In addition to one or more of the features described above, or as analternative, in further embodiments in the first phase the phase changematerial is a solid and in the second phase the phase change material isa gas.

In addition to one or more of the features described above, or as analternative, in further embodiments the phase change material is one ofwater, ethanol, and carbon dioxide.

In addition to one or more of the features described above, or as analternative, in further embodiments an exterior surface of the bladderdefines a contour of an interior surface of the composite structure whenthe bladder is filled with the phase change material.

In addition to one or more of the features described above, or as analternative, in further embodiments the flexible body further comprisesan opening for providing the phase change material to the hollow chamberand a sealing device for sealing the phase change material within thehollow chamber.

In addition to one or more of the features described above, or as analternative, in further embodiments the bladder including the phasechange material remains sealed within the at least one composite ply.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a perspective view of an example of a composite structurehaving an internal component;

FIG. 2 is a perspective view of a system for forming a hollow compositestructure according to an embodiment;

FIG. 3 is a cross-sectional view of the system of FIG. 2 for forming ahollow composite structure according to an embodiment; and

FIG. 4 is a block diagram illustrating a method of using the system ofFIGS. 2 and 3 to form a hollow composite structure according to anembodiment.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

The term “about” is intended to include the degree of error associatedwith measurement of the particular quantity based upon the equipmentavailable at the time of filing the application.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

Referring now to FIG. 1, an example of a composite structure formedhaving one or more hollow compartments is illustrated. As shown, thecomposite structure 20 is a wing of an aircraft. The wing 20 has anairfoil shape and includes at least one hollow compartment 22 definedwithin the interior of the structure 20. In the illustrated,non-limiting embodiment, the wing 20 includes three separate anddistinct compartments 22 a, 22 b, 22 c formed within the interior of thestructure 20. Adjacent compartments may be separated from one anotherand sealed at the exposed ends of the composite structure 20 by a solidrib 24. It should be understood that the composite wing structure 20illustrated and described herein is intended as an example only and thatany suitable composite structure is considered within the scoped of thedisclosure. In embodiments where the composite structure 20 has acomplex configuration and/or several internal compartments 22, it may bedesirable to manufacture the composite structure 20 in segments orportions.

With reference to FIGS. 2 and 3, an example of a system 30 for forming ahollow composite structure, such as a portion of the wing structure 20of FIG. 1 for example, is illustrated in more detail. As shown, thesystem 20 includes a bladder 32 having a sealable internal chamber 34.The bladder 32 is formed from a flexible material and is transformablebetween an inflated configuration (shown) and a deflated configuration(not shown). In the inflated configuration, the shape or contour of thebladder 32 defines at least a portion of the shape of an inner surface36 of the composite structure 20 being formed.

In an embodiment, the bladder 32 is transformed from a deflatedconfiguration to an inflated configuration by filling the internalchamber 34 of the bladder 32. As shown, the bladder 32 may include anopening 35 which fluidly couples the interior 34 of the bladder 32 withan external ambient. A plug or other sealing device 37 is removablyinstallable within the opening 35 to selectively seal the internalchamber 34 from ambient once a desired volume of material 48 has beenprovided to the bladder 32 to fill the chamber 34. As used herein theterm “filled” may represent embodiments where the volume of the internalchamber 34, in its entirety, is occupied; however, in other embodiments,the term “filled” may be used to describe embodiments where only aportion of the internal volume of the chamber 34 is occupied. Thebladder 32 may be transformed from the deflated configuration to aninflated configuration by filling the chamber 34 with a material 48 in afirst phase or state. In an embodiment, the material 48 in a first stateis a fluid, such as a liquid for example. However, in other embodiments,the material 48 in a first state used to fill the chamber 34 of thebladder 32 may be a gas, or alternatively, a solid. Examples of suitablematerials 48 that may be used to inflate the bladder 32 include, but arenot limited to water, ethanol, and carbon dioxide for example.

The material 48 used to fill the chamber 34 is selected to expand andapply a pressure to the internal surface of the bladder 32 while thecomposite structure 20 is cured. In an embodiment, the material 48 usedto fill the chamber 34 will transform from a first phase or state to asecond phase or state in response to the change in temperature presentduring the curing process. This change in phase will cause the material48 to expand, thereby creating a volumetric pressure which is evenlydistributed across the internal surface of the bladder 32. For example,a liquid selected to fill the chamber 34 will vaporize in response to anincrease in temperature used to cure the plies of the compositestructure 20. In embodiments where a solid is used to fill the chamber34, the solid may transform to either a liquid or a gas, so long as thevolume of the material 48 increases as a result of the change in state.

Further, the system 30 may additionally include an outer mold 38 formedfrom one or more pieces configured to cooperate to substantiallysurround the bladder 32 and the plurality of composite plies, shown at40, wrapped about an exterior surface of the bladder 32. An innersurface 42 of the outer mold 36 is configured to define a desired shapeof at least a portion of an outer surface 44 of the composite structure20 being manufactured. Accordingly, the bladder 32 and the outer mold 38cooperate to define the contours of the interior and exterior of thecomposite structure 20.

A method 100 of manufacturing a hollow composite structure 20 using thesystem of FIGS. 2 and 3 is illustrated in FIG. 4. The method 100includes placing a bladder 32 having the material 48 in the first statein the composite structure 20, the bladder 32 having a contourcomplementary to an interior surface of at least a portion of acomposite structure 20 to be formed from a deflated configuration to aninflated configuration, as shown in block 102. As previously described,the phase change material may be any suitable material 48 configured toexpand or increase in volume in response to an increase in temperature.The phase change material 48 used to fill the bladder 32 should beselected to achieve a suitable rate of expansion to apply a desiredpressure to the interior of the bladder 32 when heated to a temperaturerange suitable to cure the composite plies of the composite structure20. In block 104, once the bladder 32 has been filled with a phasechange material 48 in a first phase, a plurality of composite plies arewound or laid up about the exterior surface of the bladder 32 in adesired manner. After laying all of the composite plies, in block 106,an outer mold 38 is then installed about the exterior of the bladder 32and the composite plies.

In block 108, the bladder 32, composite plies, and outer mold 38 arethen heated, such as via installation within an oven or autoclave forexample, to cure the plurality of composite plies to form a solidcomposite structure 20. In response to the increased temperaturesurrounding the bladder 32 and outer mold 38, the phase change material48 within the chamber 34 of the bladder 32 transforms to a second phasehaving an increased volume compared to the first phase. As a result ofthis increased volume, the material 48 in the second state applies apressure to the interior surface of the bladder 32 during the cureprocess, i.e. while the temperature surrounding the bladder 32 and mold38 is elevated. Once the cure process is completed, and the temperaturesurrounding the bladder 32 and outer mold 38 is reduced, the phasechange material 48 will return to the first phase, thereby relieving thepressure acting on the interior surface of the composite structure 20.The composite structure 20 may then be removed from the outer mold 38.In addition, once the phase change material 48 has returned to the firstphase, the phase change material 48 and the bladder 32 may remain insidethe composite structure 20 in one embodiment. In another embodiment, thephase change material 48 may be removed from bladder 32 leaving thebladder 32 in the composite structure 20.

A bladder 32 filled with a phase change material as illustrated anddescribed herein provides a cost effective component usable in thefabrication of complex hollow composite structures having an internalgeometry. Further, the bladder is light enough that the bladder canremain within the cured composite structure 20 without a substantialweight penalty.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A method of fabricating a composite structure,comprising: laying at least one composite ply about a bladder, thebladder comprising a phase change material in a first phase having afirst volume; positioning an outer mold about the bladder and the atleast one composite ply; and curing the at least one composite ply toform the composite structure, wherein said curing causes the phasechange material contained within the bladder to change to a second phaseto expand from the first volume to a second volume and apply a pressureto an interior surface of the composite ply and press an outer surfaceof the composite ply against the outer mold to form an interior cavity,wherein the bladder is not removable from the formed interior cavity. 2.The method of claim 1, wherein curing the at least one composite plyfurther comprises changing a temperature adjacent the at least onecomposite ply.
 3. The method of claim 1, further comprising at leastpartially filling an interior chamber of the bladder with the phasechange material in the first state prior to laying the at leastcomposite ply about the bladder.
 4. The method of claim 1, wherein inthe first phase, the material is a liquid and in the second phase thematerial is a gas.
 5. The method of claim 1, wherein in the first phase,the material is a solid and in the second phase the material is a gas.6. The method of claim 1, wherein an exterior surface of the bladderdefines a contour of an interior surface of the composite structure whenin the inflated configuration.
 7. The method of claim 1, wherein aninterior surface of the outer mold defines a contour of an exteriorsurface of the composite structure.
 8. The method of claim 1, whereinafter curing the at least one composite ply is completed, the bladderincluding the material remains sealed within the at least one compositeply.
 9. The method of claim 1, further comprising removing the materialfrom the bladder while the bladder remains within the compositestructure.
 10. The method of claim 1, further comprising: removing thepressure applied by the material to the interior surface of the bladderafter curing of the at least one composite ply is complete; and removingthe material from the composite structure.
 11. A composite structurecomprising: at least one composite ply defining a cavity; a bladderarranged within the cavity such that the at least one composite ply iswrapped about the bladder, the bladder comprising: a flexible bodyoperable to define an interior surface of the composite structure, thebody having a hollow chamber; and a phase change material arrangedwithin the hollow chamber, wherein the phase change material is in afirst phase having a first volume when supplied to the hollow chamberand the phase change material is in a second phase having a secondvolume during a cure of the at least one composite ply wrapped about thebladder, wherein the second volume is expanded relative to the firstvolume, and wherein the bladder is not removable from the cavity. 12.The bladder of claim 11, wherein in the second phase, the phase changematerial is configured to apply a pressure to an interior surface of thebladder.
 13. The bladder of claim 11, wherein in the first phase thephase change material is a liquid and in the second phase the phasechange material is a gas.
 14. The bladder of claim 11, wherein in thefirst phase the phase change material is a solid and in the second phasethe phase change material is a gas.
 15. The bladder of claim 11, whereinthe phase change material is one of water, ethanol, and carbon dioxide.16. The bladder of claim 11, wherein an exterior surface of the bladderdefines a contour of an interior surface of the composite structure whenthe bladder is filled with the phase change material.
 17. The bladder ofclaim 11, wherein the flexible body further comprises: an opening forproviding the phase change material to the hollow chamber; and a sealingdevice for sealing the phase change material within the hollow chamber.18. The bladder of claim 11, wherein the bladder including the phasechange material remains sealed within the at least one composite ply.